Radiofrequency (RF) electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart of concern. A typical renal ablation procedure involves the insertion of a catheter having an electrode at its distal end into a renal artery in order to complete a circumferential lesion in the artery in order to denervate the artery for the treatment of hypertension. A reference electrode is provided, generally attached to the skin of the patient or by means of a second catheter. RF current is applied to the tip electrode of the ablating catheter, and current flows through the media that surrounds it, i.e., blood and tissue, toward the reference electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the renal artery tissue resulting in formation of a lesion within the renal artery tissue which is electrically non-conductive. The lesion may be formed in the renal artery tissue or in adjacent tissue. During this process, heating of the electrode also occurs as a result of conduction from the heated tissue to the electrode itself
Although clinical trials have indicated that renal denervation can result in a statistically significant reduction in blood pressure, challenges are associated with such procedures as conventionally performed. For example, a typical denervation procedure may involve the formation of one or more lesions at desired locations in a patient's renal vasculature intended to sufficiently affect the sympathetic nervous system so that the desired reduction in blood pressure results. However, in order to gauge success, the patient typically needs to be monitored for a significant period of time after the procedure on the order of days or even months to determine whether the desired reduction in blood pressure has been achieved. If the desired result is not obtained, the patient may need to undergo the procedure one or more times until a sufficient reduction is produced. As will be appreciated, this represents an increase in trauma to the patient, cost and recovery time.
Accordingly, it would be desirable to evaluate whether the patient's renal vasculature has been sufficiently denervated while the procedure is being performed. This disclosure satisfies this and other needs, as will be described in the following materials.